To provide better drivability and performance while maintaining fuel economy requirements, automotive designers have shifted rapidly away from carburation to injection of fuel. Especially attractive is port fuel injection (PFI, also called "multi port fuel injection") in which injectors discharge fuel into an intake runner or intake port, which delivers air to the combustion chamber or cylinder of the engine.
For accurate, precise, injection of fuel into each combustion chamber or cylinder, the injector is best located as close as possible to the intake valve. This requires the injector to operate in an environment of relatively high temperature, particularly during "hot soak", when the engine ignition system has been turned off, stopping the circulation of coolant through the engine, but leaving the hot cylinders to transfer their heat to the injector and other outer parts of the engine.
Under these conditions, the injector temperatures can reach or exceed 90.degree. C. (194.degree. F.) and carbon and varnish deposits can form on the injector internal parts, particularly the injector tip. Because of the high precision of injector parts, these deposits can restrict fuel flow. This problem, which has recently become widespread, is commonly termed "port injector plugging" and can markedly impair drivability, causing hesitation, poor fuel economy, increased exhaust emissions, and excessive stalling.
(1) Field of the Invention
The present invention relates to fuel injection systems, generally classified in Class 123, variously in subclasses 32, 139, 119, 478, 494, 436, 478, and 536-539.
(2) Description of the Prior Art
Conventional fuel injection systems are generally described in U.S. patents in Class 123, including U.S. Pat. No. 4,539,961 assigned General Motors, which shows the fuel rail port fuel injectors for delivering fuel to an engine and shows pressure regulator valve 50 for maintaining the pressure in fuel rail 22 relatively constant during engine operation.
Control systems for fuel injection are discussed in a number of patents in Class 123, including U.S. Pat. No. 4,501,249 assigned to Hitachi, which details a control apparatus for controlling the amount and timing of fuel injection with the aid of a microcomputer reading inputs from a hot-wire type flow sensor for detecting air flow velocity within an intake air passage of an internal combustion engine.
U.S. Pat. No. 4,347,825 assigned Nissan electrifies fuel to atomize it into fine fuel particles and avoid attachment onto the surrounding wall of the air intake.
A diagram of a conventional fuel injector is shown in FIG. 2 of U.S. Pat. No. 4,020,802 assigned Nipon Soken. This figure shows the injector assembly for (a) near the intake valve 20(a), and discharging directly into the intake port 19(a), through which air flows through the valve into the combustion chamber.
To address the problem of avoiding port fuel deposits, a number of solutions have been tried including gasoline additives e.g. those manufactured by DuPont and Lubrizol Corporations, Ethyl, Nalco, Chevron, Mobil, Amoco Chemical, Exxon, etc.
Rochester Division of General Motors Corporation's, Multec Injector System, shows a method for providing a multiplicity of fuel-spray cones into the intake port. Allied Automotive, formerly Bendix Corporation, has recently introduced their "Deka" injector, providing similar multi-spray cones of fuel injected into the intake port. Both of these injector configurations are designed to avoid, to some extent, the susceptibility to plugging of the injector.
Rather than requiring additives to be inserted into all of the fuel to be burned by an engine, or requiring redesign of the individual injectors, the present invention provides a change in system conditions which has been found to substantially reduce deposits with relatively minor modification of the fuel system components. The simplicity of the present invention also permits it to be readily inserted into the millions of fuel-injected internal combustion engines which have already been manufactured.